Export JSON to file on LAMP

#fetchAPI #javascript #json #php

September 18, 2018
by Matteo Bertozzo

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It’s really easy to manipulate JSON with JavaScript. But what if we want to save it as a file on a LAMP server?

Basically, what we want to achieve is to store our client-generated JSON on the server, except we don’t have an existing API to call. And since we suppose to be on a LAMP server, no Javascript for server-side code!

The only thing to do is to create a PHP script that will be called by JavaScript taking advantage of the Fetch API.

Let’s start by creating a save.php file and writing in it what follows:

  $content = trim(file_get_contents("php://input"));
  //retrieve the current file path  
  $base_dir = dirname(__FILE__);

  //open the file data.json and overwrite it with content
  //if the file does not exist, create it
  $file = fopen($base_dir."/data.json","w");
  echo fwrite($file,$content);

Here we’re using php://input, that is a read-only stream that allows us to read raw data from the request body. It returns all the raw data after the HTTP-headers of the request, regardless of the content type. In our case, the content type will be application/json: this is why we’re not using, as an alternative, $_POST. This PHP superglobal, as a matter of fact, is only supposed to wrap data that is either application/x-www-form-urlencoded (such as forms) or multipart/form-data-encoded (such as file uploads).

To be sure of what’s been retrived let’s add a check:

  $contentType = isset($_SERVER["CONTENT_TYPE"]) ? trim($_SERVER["CONTENT_TYPE"]) : '';

  if ($contentType === "application/json") {
    $content = trim(file_get_contents("php://input"));
    $base_dir = dirname(__FILE__);

    $file = fopen($base_dir."/data.json","w");
    echo fwrite($file,$content);

Now, the last part is to call this script from inside JavaScript:

fetch("save.php", {
  method: "post",
  mode: "same-origin",
  credentials: "same-origin",
  headers: {
    'Accept': 'application/json',
    'Content-Type': 'application/json'
  body: JSON.stringify(the-content)
.then((response) => {
  console.log = "Dati inviati!";

In this case, the-content is the variable holding the JSON we want to save.

And that’s all!